libstdc++
atomicity.h
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1 // Support for atomic operations -*- C++ -*-
2 
3 // Copyright (C) 2004, 2005, 2006, 2008, 2009 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
10 
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU General Public License for more details.
15 
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
19 
20 // You should have received a copy of the GNU General Public License and
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
24 
25 /** @file atomicity.h
26  * This is an internal header file, included by other library headers.
27  * You should not attempt to use it directly.
28  */
29 
30 #ifndef _GLIBCXX_ATOMICITY_H
31 #define _GLIBCXX_ATOMICITY_H 1
32 
33 #include <bits/c++config.h>
34 #include <bits/gthr.h>
35 #include <bits/atomic_word.h>
36 
37 _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
38 
39  // Functions for portable atomic access.
40  // To abstract locking primitives across all thread policies, use:
41  // __exchange_and_add_dispatch
42  // __atomic_add_dispatch
43 #ifdef _GLIBCXX_ATOMIC_BUILTINS_4
44  static inline _Atomic_word
45  __exchange_and_add(volatile _Atomic_word* __mem, int __val)
46  { return __sync_fetch_and_add(__mem, __val); }
47 
48  static inline void
49  __atomic_add(volatile _Atomic_word* __mem, int __val)
50  { __sync_fetch_and_add(__mem, __val); }
51 #else
52  _Atomic_word
53  __attribute__ ((__unused__))
54  __exchange_and_add(volatile _Atomic_word*, int);
55 
56  void
57  __attribute__ ((__unused__))
58  __atomic_add(volatile _Atomic_word*, int);
59 #endif
60 
61  static inline _Atomic_word
62  __exchange_and_add_single(_Atomic_word* __mem, int __val)
63  {
64  _Atomic_word __result = *__mem;
65  *__mem += __val;
66  return __result;
67  }
68 
69  static inline void
70  __atomic_add_single(_Atomic_word* __mem, int __val)
71  { *__mem += __val; }
72 
73  static inline _Atomic_word
74  __attribute__ ((__unused__))
75  __exchange_and_add_dispatch(_Atomic_word* __mem, int __val)
76  {
77 #ifdef __GTHREADS
78  if (__gthread_active_p())
79  return __exchange_and_add(__mem, __val);
80  else
81  return __exchange_and_add_single(__mem, __val);
82 #else
83  return __exchange_and_add_single(__mem, __val);
84 #endif
85  }
86 
87  static inline void
88  __attribute__ ((__unused__))
89  __atomic_add_dispatch(_Atomic_word* __mem, int __val)
90  {
91 #ifdef __GTHREADS
92  if (__gthread_active_p())
93  __atomic_add(__mem, __val);
94  else
95  __atomic_add_single(__mem, __val);
96 #else
97  __atomic_add_single(__mem, __val);
98 #endif
99  }
100 
101 _GLIBCXX_END_NAMESPACE
102 
103 // Even if the CPU doesn't need a memory barrier, we need to ensure
104 // that the compiler doesn't reorder memory accesses across the
105 // barriers.
106 #ifndef _GLIBCXX_READ_MEM_BARRIER
107 #define _GLIBCXX_READ_MEM_BARRIER __asm __volatile ("":::"memory")
108 #endif
109 #ifndef _GLIBCXX_WRITE_MEM_BARRIER
110 #define _GLIBCXX_WRITE_MEM_BARRIER __asm __volatile ("":::"memory")
111 #endif
112 
113 #endif
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